Multiple redox-active cyano-substituted organic compound integrated with MXene for high-performance flexible aqueous K-ion battery

Abstract

Aqueous alkali-ion batteries are a kind of risk-free and low-cost energy storage devices for portable equipment and wearable products. Even though phenazine-based organic compounds have π-conjugated aromatic structures and contain N heteroatoms with redox-active centers, the limited capacity performance still hinders their application as the electrode material for aqueous alkali-ion batteries. Herein, we firstly designed a novel cyano-substituted diquinoxalinophenazine (6CN-DQPZ) organic compound, which was further integrated with MXene to construct a self-supported and binder-free 6CN-DQPZ@MXene electrode. Theoretical calculation and in-situ Raman analysis demonstrate that the introduction of cyano electron-withdrawing groups not only optimizes the electronic structure of 6CN-DQPZ to enhance its electrochemical activity, but also provides additional redox-active sites for 6CN-DQPZ upon K+ uptake/removal, thereby endowing a rapid, ultra-stable and efficient aqueous K+ storage behavior for the 6CN-DQPZ@MXene electrode, especially a considerably large reversible capacity of 477.6 mAh cm−3 (or 238.8 mAh/g) and exceptional cycle performance with a high capacity retention of ∼ 98.9 % over 2000 cycles. For actual applications, a high-performance flexible aqueous K-ion battery (AKIB) has been fabricated with considerable energy/power characteristics and long lifespan under the straight and bending states, revealing its potential application as a reliable and efficient flexible energy storage device for portable/wearable electronics.